The present invention relates to a light beam scanning apparatus used for image formation apparatuses such as a digital copier, a laser printer, etc. which use a laser light beam to scan and expose a photoconductor drum and form an electrostatic latent image on the photoconductor drum.
In recent years, there have been developed various digital copiers which are equipped with a light beam scanning apparatus to perform scanning and exposure using a laser light beam (hereafter simply referred to as the light beam) and use an electrophotographic process to form an image.
Recently, a multi-beam digital copier is developed for increasing an image formation speed. Such multi-beam digital copier is provided with a light beam scanning apparatus which simultaneously scans a plurality of lines by using a plurality of light beams.
In order to form a high-quality image, a digital copier mounted with an optical unit using the above-mentioned light beam scanning apparatus controls a light beam exposure position in the horizontal scan direction and a light beam passage position in the vertical scan direction.
For example, a conventional light beam scanning apparatus detects a light beam by using a sensor arranged on an exposure surface or a position level to the exposure surface. The apparatus controls light beams based on a sensor""s detection output.
However, the following problems arise when improving the light beam""s detection accuracy and control accuracy.
Improving the light beam""s detection accuracy may require a high-resolution circuit for processing a light beam detection output. Such circuit may make the light beam control difficult.
An offset in the circuit for processing a light beam detection output may disable provision of the intended detection accuracy or cause a processing error.
The flare generated around a light beam may cause an error for the light beam passage position and the light beam control.
A vibration etc. may change the light beam passage position and disable the accurate detection of the light beam passage position.
If these causes make it impossible to provide the intended detection accuracy and the control accuracy for a light beam, there is a problem of deteriorating the quality of an image formed by the light beam. If the light beam""s detection accuracy and control accuracy cannot be improved, it becomes difficult to provide a high-quality image formed by the light beam.
It is therefore an object of the present invention to provide a light beam scanning apparatus capable of improving the light beam""s detection accuracy and control accuracy and providing a high-quality image formed by the light beam.
A light beam scanning apparatus according to the present invention controls a light beam and comprises: a light source to generate the light beam; a scanning section to scan the light beam generated from the light source; a pair of sensors comprising a plurality of photoelectric conversion elements, wherein output from one sensor increases and output from the other sensor decreases according to a change of the light beam scan position in the vertical scan direction; and a control section which controls the light beam scan position in the vertical scan direction so that a difference between outputs from the pair of sensors becomes a target value, wherein the light beam volume output from the light source is set to a first light volume and the light beam volume output from the light source is set to a second light volume larger than the first light volume.
A light beam scanning apparatus according to the present invention controls a light beam and comprises: a light source to generate the light beam; a scanning section to scan the light beam generated from the light source; a sensor which comprises a plurality of photoelectric conversion elements and outputs a signal corresponding to the light beam scan position in the vertical scan direction; a comparator which compares an output from the sensor with upper and lower bounds as a target value for that output; a control section which controls the light beam scan position in the vertical scan direction based on a comparison result from this comparator so that an output from the sensor falls between the lower bound and the upper bound; and a single setup section which supplies the comparator with the lower bound and the upper bound specified by the control section.
A light beam scanning apparatus according to the present invention controls a light beam and comprises: a light source which generates the light beam having a specified diameter; a scanning section to scan the light beam generated from the light source; a pair of sensors which comprise a plurality of photoelectric conversion elements and are arranged so that the sensors are symmetrical with reference to a control target for the light beam""s scan position in the vertical scan direction and an entire width in the vertical scan direction becomes smaller than the light beam""s specified diameter in the vertical scan direction; and a control section which controls a peak position of the light volume for the light beam scanned by the scanning section in the horizontal scan direction based on a difference between outputs from the pair of sensors so that the peak position is aligned to the control target position.
A light beam scanning apparatus according to the present invention controls a light beam and comprises: a light source to generate the light beam; a scanning section to scan the light beam generated from the light source; a sensor which comprises a plurality of photoelectric conversion elements and outputs a signal corresponding to a light beam scan position in the vertical scan direction; memory which stores an output value from the sensor each time the scanning section scans the light beam in the horizontal scan direction; and a determination section which determines the light beam scan position based on a plurality of output values store in this memory.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.